1. Field of the Invention
This invention relates to an apparatus and method for hydrolyzing cyanide ions in waste water, and more particularly to an improved apparatus and method for hydrolyzing cyanide ions in waste water into ammonia and formate by instantly and uniformly heating the liquid, for example, by injecting a hot fluid under pressure to uniformly heat the cyanide-containing liquid before it is fed into a reactor.
2. Description of the Prior Art
Various methods have been developed to hydrolyze cyanide ions which are the by-products of various industrial processes, including the reduction process for obtaining pure aluminum metal from alumina. For example, according to the patentees of U.S. Pat. No. 4,042,502 (Schmidt), cyanide ions in cyanide ion containing wastes can be oxidized to less harmful substances at high temperatures and pressures in a batch reactor. The process contemplates subjecting the liquid to a temperature shock, and then passing the cyanide-containing solution through a tubular batch process reactor at a pressure of between about 40 and 140 atm. Concentrated sulfuric acid is mixed with the cyanide solution.
U.S. Pat. No. 4,812,243 (Brandenburg) discloses a second approach to decomposition of cyanide ions in cyanide ion containing liquids. The continuous wet air oxidation treatment process in this patent appears to involve introducing a preheated, pressurized oxygen containing gas with water for dilution into a vertical bubble-type reactor where wet oxidation occurs. The waste, water and gas mix within the reactor and are raised to a temperature between about 200.degree. to 370.degree. C., at pressures between 300 and 2000 p.s.i.g. Brandenburg acknowledges, however, that the process seems to engender rapid scale build up. To remedy this, Brandenburg suggests providing dual reactors, allowing one to be shut down to remove scale, while the other reactor continues operation.
The high solids content of the cyanide-containing waste liquid seems to present particularly difficult scale accumulation problems, requiring the operator to frequently shut the reactor down to remove scale. An attempt to provide a continuous reactor which can continuously hydrolyze cyanide ions in a liquid into ammonia and formate is discussed in Kimmerle et al., "Cyanide Destruction in Spent Potlining," Light Metals 89, pp. 387-394 (P. G. Campbell (ed.)). The authors appear to propose a tubular reactor heated by a coaxial heat exchanger which hydrolyzes cyanide and ferrocyanide ions contained in an alkaline solution of spent potlining leachate. The use of heat exchangers, particularly coaxial heat exchangers, however, leads to such rapid scaling of the tubular reactor that the flow in the reactor is soon reduced to ineffective rates, necessitating shut down to remove accumulated scale.
None of the foregoing approaches has provided a satisfactory solution to the problem of cyanide ion detoxification in a continuous reactor not susceptible to scale build up.